This may help with that. Simplify3D needs a small change made to the “Flow Control” setting located in the “Advanced” section of the “Communications” tab which can be found in the “Firmware Configuration” settings. The “Flow Control” drop-down has three options:

No Flow Control

Hardware Flow Control (RTS/CTS)

Software Flow Control (XON/XOFF)

Choosing either the hardware or software options seems to work.
The only difference made in the S3D firmware profile is to the “Flow Control” setting which is set to “Hardware Flow Control (RTS/CTS)”.